The present invention relates to a bearing apparatus comprising: a first member; a second member; rolling elements rotatably interposed between the first and second members to thereby effect relative movement therebetween; and a seal device for sealing at least a portion of a clearance defined between the first and second members.
Particularly, a first aspect of the present invention relates to a linear motion apparatus, which is one example of the bearing device, such as a linear guide apparatus and a ball screw apparatus, and more particularly to an improvement in a contact rubber seal device serving as a seal device.
A second aspect of the present invention relates to a water pump bearing, which is one example of the bearing apparatus and is suitable for use with a water-cooled automobile engine, and more particularly to a bearing having a seal device for preventing entry of water or moisture into a bearing supporting a rotary shaft of a water pump and preventing leakage of grease from the inside of the bearing.
A third aspect of the present invention relates to a rolling bearing, which is an example of the bearing apparatus, and more particularly to an improvement in a rubber seal device to be used in the bearing apparatus.
For instance, a linear guide apparatus to be used as a linear motion guide apparatus and a ball screw apparatus to be used as a linear motion drive apparatus have hitherto been known as typical ones of linear motion apparatus.
As shown in FIG. 10, the linear guide apparatus is equipped with a guide rail (functioning as interior member) 1 extending in its longitudinal direction; and a slider 2 (functioning as exterior member) sliding on the guide rail 1 so as to be movable in an axial direction while a predetermined clearance is provided between the slider 2 and the guide rail 1.
A pair of rolling-element contact grooves 3 are formed on either side surface of the guide rail 1 so as to extend in the axial direction thereof. A pair of linear rolling-element contact grooves (not shown) opposing the rolling-element contact grooves 3 are formed in the interior surface of each wing 4 provided on either side of a slider main body 2A of the slider 2.
A plurality of steel balls (not shown) serving as rolling elements are rotatably provided between the rolling-element grooves 3 formed in the guide rail 1 and the counterpart grooves formed in the slider 2, which mutually oppose. The slider 2 can travel along the guide rail 1 in the axial direction by means of rolling action of the steel balls. As the slider 2 travels, the steel balls interposed between the guide rail 1 and the slider 2 rotate and shift to the end of the slider main body 2A of the slider 2. In order to continuously move the slider 2 in the axial direction, an infinite number of steel balls must be circulated.
To this end, linear rolling-element channels (not shown) are formed so as to axially penetrate through each of the wings 4 of the slider main body 2. An end cap 2B serving as a rolling-element circulating component is provided at either longitudinal end of the slider main body 2A. A rolling-element circulation R section having a semi-circular-shaped curve is formed in each end cap 2B so as to establish mutual communication between the rolling-element grooves and the rolling-element passages, thus constituting an endless rolling-element circulation railway.
As shown in FIG. 11, a side seal member 5 (a contact seal having negative clearance with respect to the guide rail 1) is attached to either end of the slider 2 for sealing an opening of a clearance defined between the guide rail 1 and the slider 2. An underseal member 6 is affixed to the underside of the slider 2.
Rubber material such as acrylonitrile butadiene (NBR) is commonly used for the seal members 5, 6 and is formed integrally with reinforcing material, such as a steel plate. Particularly, when the seal member requires chemical resistance or heat resistance, fluoro rubber [such as FKM; vinylidenefluoride-hexafluoropropylene-based fluoro rubber or vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene-based fluoro rubber] is often used as rubber material. In the drawing, reference numeral 7 indicates a grease nipple.
Although not shown in the drawing, a ball screw apparatus, which is a linear motion apparatus, converts rotation of a screw shaft (or ball screw nut) into axial displacement of a ball screw nut (or screw shaft), through a plurality of balls (rolling elements) interposed between a helical screw groove formed in the outer circumferential surface of a screw shaft (inner member) and a helical screw groove formed in an inner circumferential surface of a ball screw nut (outer member). For example, a plastic seal member is attached as a contact seal device to either end of the ball screw nut, thereby preventing entry of extraneous matter into the ball screw nut from the outside or leakage to the outside of a lubricant from the inside of the ball screw nut.
The contact seal device is usually formed of resin material, such as polyacetal resin, into the shape of a ring. A thread to engage with the screw thread of the screw shaft is formed on an interior diameter section of the contact seal device, and a notch (discission) is formed in the contact seal device for radially cutting.
The notch is opened to open the ring widely, and the thus-opened contact seal device is fitted around the screw shaft. A lockscrew is screwed into a ball screw nut from an outer circumferential surface at the end thereof. The outer-diameter surface of the contact seal device is pressed inwardly, whereby the contact seal device is secured to the end of the ball screw nut.
However, the contact seal device employed in the related-art linear guide apparatus and that employed in the related-art ball screw apparatus involve the following problems.
First, a problem of the contact seal device employed in the linear guide apparatus will be described. The rotating speed of a main spindle of a machine tool employing a linear guide apparatus has recently been increased. In connection with a tool, a dramatic leap has been achieved in development of highly heat resistant material or a coating technique, in an attempt to increase the speed and efficiency of cutting work. In association with such a development, a synthetic cutting coolant of soluble type, which can be subjected to sewage processing by means of complete dissolution into water, has come to replace a related-art water-soluble cutting fluid of emulsion type, in order to make full use of all the capabilities of the cutting fluid. Namely, a cooling property for absorbing a large quantity of heat developing in the vicinity of a cutting point, permeability for reaching a cutting point momentarily, and lubricity at a high-temperature, high-pressure cutting point.
The major feature of the soluble-type synthetic cutting coolant lies in that a large number of various types of additive agents, such as amine, are added to the coolant in order to improve permeability. Hence, the coolant is highly permeable to rubber material, and the rubber material is susceptible to deformation, such as expansion or softening. Consequently, the rubber strength of a slide member (e.g., a rubber lip section) of the contact seal device belonging to the linear guide, which apparatus is used in an environment in which the apparatus is splashed with a soluble-type synthetic cutting coolant, becomes weak. Concurrently, a region of the seal member to be fastened becomes greater, and as a result abrasion of the seal member is accelerated. This results in a drop in sealing property of the seal member, which may deteriorate the life of the linear guide apparatus.
Particularly, when the rubber material of the seal member is made of FKM (i.e., vinylidenefluoride-hexafluoropropylene-based fluoro rubber or vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene-based fluoro rubber), an amino-based additive is considered to induce removal of HF (hydrogen fluoride) at a plurality of sites of vinylidene fluoride which are present in a structure of FKM, thereby deteriorating the rubber material and reducing the rubber strength of the seal member.
In the ball screw apparatus, a ring-shaped seal device is usually secured to a ball screw nut by means of a lockscrew. Hence, the clearance of engagement between the screw groove of the screw shaft and a projection of the seal device depends on a dimensional relationship between the screw groove of the screw shaft and the seal device. Hence, the clearance of engagement does not become zero at all times. Depending on the requirements for use of the ball screw apparatus, a sufficient sealing characteristic may not be obtained. Consequently, extraneous matter, such as cutting dust, becomes more likely to enter the ball screw nut, potentially causing seizing up of the ball screw apparatus.
If a rubber seal member is used in place of the plastic seal member, as in the case of the contact seal device of the linear guide apparatus, in order to improve the sealing property of the ball screw apparatus, the same problems as those that have arisen in the linear guide apparatus are considered to occur.
The first aspect of the present invention has been conceived to solve the problems.
Hereinafter, one of typical examples of a conventional bearing device for a water pump will be hereinafter explained.
As shown in FIG. 12, a water pump 130 for circulating engine cooling water through compression usually comprises a rotating shaft 112 having an impeller 132 secured thereon, and the rotating shaft 112 is supported in a casing 138 by means of a plurality of rolling bearings 110 spaced apart from each other in the axial direction. The cooling water is hermetically sealed by a mechanical seal 140 provided between the impeller 132 and the bearings 110. The surfaces of the bearings 110 for water pump (often called simply as xe2x80x9cbearingsxe2x80x9d) remaining sliding contact with the rotating shaft 112 of the mechanical seal 140 are in a water lubricated state. In this state, steam will leak and enter the bearings 110, and the bearings 110, 110 are deteriorated by the steam. A seal device is provided on the part of the bearing 110 opposing the impeller 132 for preventing entry of steam into the bearing 110 from the impeller 132 and leaking of lubrication grease sealed in the bearing 110. Another seal device is also provided on the part of the bearing 110 opposing a driven side 131 for preventing entry of dust from the outside and leaking of the lubrication grease sealed in the bearing 110.
For instance, the seal device provided on the part of the bearing 110 opposing the impeller 132 has a structure shown in an axial cross-sectional view of FIG. 13. As shown in FIG. 13, the bearing 110 comprises an outer ring 110a; a rotating shaft 112 constituting an inner ring; balls 110b sandwiched between the outer ring 110a and the rotating shaft 112; and a retainer 110c for holding the balls 110b. A seal device 400 comprises a sealing plate 115 and a thrower 120. The sealing plate 115 is provided in a seal groove 110d formed in the axial end portion of the outer ring 110a. The sealing plate 115 comprises a core 115a and elastic material 115b, and the resilient member 115b comprises three lip sections 115c, 115d, and 115e. The core 115a has a reversed L-shape cross-sectional profile and is squeezed into the seal groove 110d of the outer ring 110a. The elastic material 115b is provided in intimate contact with the outer surface of the core 115a. The elastic material 115b is made of nitril rubber or standard fluoro rubber having superior heat resistance (e.g., vulcanizable fluoro rubber composition containing vinylidenefluoride-hexafluoropropylene copolymer or vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene terpolymer). The elastic material 115b has a bifurcated cross sectional profile. A main lip section 115e constituting one of the bifurcated portion obliquely extends in the lower right direction, and a sub-lip section 115d constituting the remaining of the bifurcated portion obliquely extends in the lower left direction. A cylindrical third lip section 115c is formed in the middle of the core 115a so as to extend from the elastic material 115b in the right direction in the drawing.
The stainless thrower 120 is provided on the rotating shaft 112. The thrower 120 comprises a small cylinder 120c to be closely fitted to the rotating shaft 112; a large cylinder 120a concentrically enclosing the small cylinder 120c, and a flange 120b interconnecting the small cylinder 120c and the large cylinder 120a with in the radial direction. The third lip section 115c of the elastic material 115b is in contact with the outer periphery of the large cylinder 120a of the thrower 120, thereby constituting a hermetic seal. The main lip section 115e is in contact with the outer periphery of the small cylinder 120c, thereby constituting a hermetic seal. The sub-lip section 115d is in contact with the outer circumferential surface of the rotating shaft 112, thus constituting a hermetic seal.
When steam or water droplets of cooling water have splashed over the seal device 400 from the outside, the outer circumferential surface of the thrower 120 receives the steam or water droplets, thereby protecting the seal plate 115 from a splash of cooling water. In this way, expansion or deformation of the sealing plate 115 (particularly the third lip member 115c) can be diminished. In contrast, the grease sealed in the bearing 110 is sealed by the sub-lip section 115d and the main lip section 115e of the sealing plate 115, thereby preventing leakage of grease to the outside.
In association with a recent increase in performance and output of an engine, temperature conditions of the engine become more harsh. In some cases, the ambient temperature of the bearing exceeds 120xc2x0 C. or thereabouts. When nitril rubber is used as elastic material of the seal device of the bearing 110, a resilient material becomes hard and deteriorated by means of heat, thus losing elasticity. In the worst case, cracks arise in the lip section, which may deteriorate the sealing performance of the seal device. A limit of heat resistance of standard fluoro rubber is 200xc2x0 C. or higher. Even the above-described temperature conditions pose no problem in heat resistance. However, if the fluoro rubber comes into contact with an additive contained in the cooling water, the rubber may be deteriorated and deformed, thus losing sealing performance.
As elastic material for a seal device of a related-art water pump bearing, hydrogenated nitril rubber described in Japanese Patent Unexamined Publication No. Hei. 11-193795 has hitherto been known. Since the limit of heat resistance of hydrogenated nitril rubber is 150xc2x0 C., the rubber poses no problem even under the foregoing temperature conditions. However, the nitril rubber becomes deformed upon contact with an additive contained in cooling water, although the rubber is deformed less than standard fluoro rubber. Hence, the sealing performance of the seal device may decrease. Hence, the performance of the hydrogenated nitril rubber cannot be said to be sufficient.
The second aspect of the present invention aims at solving the problem.
Hereinafter, one typical example of a conventional rolling bearing will be explained.
A rubber seal, which is integrally formed from rubber such as acrylonitrile butadiene (NBR) or acrylic rubber and a metal reinforcing member such as a steel plate, has hitherto been usually used as a rubber seal device for a rolling bearing. Particularly in a case where chemical resistance or heat resistance is required, common fluoro rubber (FKM); e.g., vinylidenefluoride-hexafluoropropylene-based fluoro rubber or vinylidenefluoride hexafluoropropylene-tetrafluoroethylene-based fluoro rubber, is often used.
However, the related-art rolling bearing yields the following problems associated with a rubber seal device.
The rotating speed of a main spindle of a machine tool employing a number of pieces of rolling bearing has recently been increased. In connection with a tool, a dramatic leap has been achieved in development of highly heat resistant material or a coating technique, in an attempt to increase the speed and efficiency of cutting work. In association with the development, a cutting point is increased to a higher temperature. Hence, demand exists for cutting oil having higher cooling performance and permeability for reaching a cutting point momentarily.
In order to make full use of the capabilities of the cutting fluid, such as lubricity at a high-temperature, high-pressure cutting point, a synthetic cutting coolant of soluble type, which is completely dissolved into water, has come to replace a related-art water-soluble cutting fluid of emulsion type. The soluble-type cutting coolant is advantageous even in terms of ease of disposal of wastewater.
A large quantity of various types of additive agents, such as amine, are added to the soluble-type synthetic cutting coolant in order to improve permeability. Hence, when the coolant has come into contact with a rubber seal device, the rubber material is susceptible to deformation, such as expansion or softening. Consequently, the rubber strength of a lip section of the contact seal device becomes weak. Particularly, a lip section of contact type is greatly affected, and a region of the seal member to be fastened becomes greater. As a result, abrasion of the seal member is accelerated, resulting in a deterioration in sealing property of the seal member, which may shorten the life of the rolling bearing. Particularly, when the rubber material of the seal member is made of FKM, an amine-based additive easily induces removal of HF (hydrogen fluoride) at a plurality of sites of vinylidene fluoride which are present in a structure of KM, thereby deteriorating the rubber material and reducing the rubber strength of the seal member.
A large quantity of amine-based additive is used in an automobile coolant or the like, and similar problems are expected to arise.
A compound constituting the amine-based additive is contained in thermal decomposition products which are gradually produced when urea-based grease is used at high temperatures. Hence, even in a situation in which an amine-based additive is used as a coolant-and does not come into contact with a rolling bearing, if urea-based grease is sealed, similar problems may arise.
The third aspect of the present invention has been conceived in view of the foregoing situation.
It is an object of the present invention to solve at least one of the above-mentioned problems in the conventional techniques.
The object of the present invention can be achieved by a bearing apparatus comprising:
a first member;
a second member;
rolling elements rotatably interposed between the first and second members to thereby effect relative movement therebetween; and
a seal device for sealing at least a portion of a clearance defined between the first and second members, the seal device comprising a rubber portion made of fluoro rubber composition containing at least one of vinylidenefluoride-tetrafluoroethylene-polypropylene copolymer (terpolymer) and tetrafluoroethylene-polypropylene copolymer (bipolymer).
In an embodiment of the above-mentioned bearing apparatus, it is preferable that the bearing apparatus is a linear motion apparatus, the first member is a guide rail or screw shaft of the linear motion apparatus, and the second member is a slider or nut of the linear motion apparatus.
Further, in an embodiment of the above-mentioned bearing apparatus, it is preferable that the bearing apparatus is a rolling bearing, the first member is an outer ring of the rolling bearing, and the second member is an inner ring of the rolling bearing.
In an embodiment of the above-mentioned bearing apparatus, it is preferable that the seal device further comprises:
a reinforcing member integrally formed with the rubber portion.
Moreover, in an embodiment of the above-mentioned bearing apparatus, it is preferable that the bearing apparatus is a water pump bearing, the first member is an outer ring secured on a casing of the water pump bearing, the second member is a rotary shaft having a drive section at one end thereof and an impeller at the other end thereof, and the seal device is fastened to one end of the outer ring.
In addition, in an embodiment of the above-mentioned bearing apparatus according to the present invention, it is preferable that the at least one of vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer and tetrafluoroethylene-polypropylene copolymer is vulcanizable.
It is an object of the first aspect of the present invention to provide a linear motion apparatus which has high chemical resistance against a chemical such as soluble-type synthetic coolant containing-a large quantity of amine-based additive and which can ensure a long life even when used in a splash of the chemical.
In order to achieve the object, the first aspect of the present invention provides a linear motion apparatus comprising: an exterior member; an interior member disposed so as to oppose the exterior member through a clearance; a plurality of rolling elements which are rotatably interposed between the exterior and interior members and cause the exterior member to move relative to the interior member; and a seal device for sealing an opening of the clearance, wherein
a seal member of the contact seal device is constituted of a fluoro rubber composition basically comprising at least one of copolymers that is vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer or tetrafluoroethylene-polypropylene copolymer.
The fluoro rubber composition according to the present invention comprises various additives, such as various types of fillers, a vulcanized additive, and processing aids, in addition to a rubber stock; that is, vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer or tetrafluoroethylene-polypropylene copolymer. The rubber material composition is preferably used as a material for the seal device.
In order to manufacture a rubber feedstock; that is, vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer or tetrafluoroethylene-polypropylene copolymer, there can be adopted any of various polymerization methods, such as a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, and a solution polymerization method. Any one of a catalytic polymerization method using a free radical initiator, an ionizing radiation polymerization method, and a redox-based polymerization method is adopted, as required.
In order to facilitate vulcanization of vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer by an organic peroxide, a carbon-carbon double bond may be introduced to the principal chain of a polymer, acting as a polymerization site, through removal of hydrogen fluoride; or iodine-containing or bromine-containing monomer may be copolymerized with the principal chain of the polymer. Since the rubber feedstock contains a vinylidene fluoride site, the rubber feedstock acquires a good vulcanization characteristic without introduction of the vulcanization site, which would usually be effected for vulcanizing an organic peroxide, so long as at least either a di-metal-hydride or a di-metal-oxide, and an organic onium compound are mixed with the rubber feedstock. Thus, a vulcanized material having superior physical properties can be produced.
Desirable proportions in which three monomers are to be polymerized comprise 1 to 30 mol. % vinylidene fluoride (more preferably, 2 to 5 mol. % vinylidene fluoride), 40 to 70 mol. % tetrafluoroethylene, and 30 to 60 mol. % polypropylene. Resistance to a chemical, such as amine, and a vulcanization characteristic are greatly dependent on a proportion of polymerization of vinylidene fluoride. In view of a vulcanization characteristic, a larger proportion of vinylidene fluoride is preferable. However, an excessive proportion of vinylidene fluoride results in corresponding deterioration of chemical resistance. If chemical resistance is pursued at the expense of the vulcanization characteristic, a desirable proportion of vinylidene fluoride is 2 to 5 mol. %.
Vinylidene fluoride does not exist in the structure of tetrafluoroethylene-polypropylene copolymer. Hence, tetrafluoroethylene-polypropylene copolymer is inferior to vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer in terms of a vulcanization characteristic. However, iodine-containing or bromine-containing monomer is copolymerized with the polymer so that an organic peroxide can be vulcanized. Hence, vulcanization of tetrafluoroethylene-polypropylene copolymer becomes feasible.
Desirable proportions of copolymerization of tetrafluoroethylene-polypropylene copolymer comprise 40 to 70 mol. % tetrafluoroethylene, and 30 to 60 mol. % polypropylene.
As a filler for reinforcing purpose, 20 to 70 parts by weight of carbon black, talc, wollastonite, or Mistron Paper is preferably added to 100 parts by weight of rubber feedstock. Since silica and clay are acidic and cause delay in vulcanization, they are not preferable.
An organic peroxide is used as a vulcanizing agent. More specifically, dicumyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy) hexane, benzoyl peroxide, or 1,3-bis-(t-butylperoxy)-diisopropylbenzene is preferably added in an amount of 0.5 to 10 parts by weight to 100 parts by weight of rubber feedstock. In the case of vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer, polyamine vulcanization or polyol vulcanization is a possible alternative to peroxide vulcanization by an organic peroxide.
Unsaturated multifunctional compounds are used as a vulcanizing agent. More specifically, polyallyl compounds such as triallyl isocyanurate or triallyl cyanurate, or methacrylate compounds such as trimethylolpropanetrimethacrylate are preferably added in an amount of 0.5 to 10 parts by weight to 100 parts by weight of rubber feedstock.
In the case of vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer, hydrides and oxides, such as those of magnesium, calcium, lead, and zinc, can be mentioned as di-metal-hydride or di-metal-oxide to be used as a vulcanizing agent. Preferably, the hydride or oxide is added in an amount of 1 to 20 parts by weight to 100 parts by weight of rubber feedstock.
In the case of vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer, an organic onium compound to be added as a vulcanizing agent promotes reaction for removing hydrogen fluoride from rubber during vulcanization, thus effecting smooth vulcanization of rubber. Particularly, fatty acid quaternary ammonium hydrogensulfate having a carbon number of 1 through 20 is preferable. More specifically, there can be mentioned tetrabutylammonium hydrogensulfate, tetramethylammonium hydrogensulfate, tetraethylammonium hydrogensulfate, tridecylmethylammonium hydrogensulfate, or trimethylbenzylammonium hydrogensulfate. Preferably, the hydrogensulfate is added in an amount of 0.3 to 5 parts by weight to 100 parts by weight of rubber feedstock.
In relation to the hardness of a rubber material composition according to the present invention, the spring hardness measured by a duro-meter A scale preferably falls within a range of 60 to 90, in terms of a sealing and follow-up property obtained when the rubber material composition is applied to the contact seal device. If the spring hardness assumes a value of less than 60, the rubber lip section of the seal member of the contact seal device becomes deformed to a greater extent than required when the slider of the linear guide apparatus or the ball screw nut of the ball screw apparatus linearly travels back and forth. As a result, frictional resistance often becomes greater. This sometimes increases frictional force experienced at the time of movement of the slider or the ball screw nut, thereby hindering smooth reciprocal movement of the slider or ball screw nut.
In contrast, when the spring hardness exceeds a value of 90, rubber elasticity decreases, thereby deteriorating a follow-up characteristic or sealing characteristic of the rubber lip section of the seal member during reciprocal movement. When the contact seal device is used in an environment rich in extraneous matter, the contact seal device is susceptible to disparities in life.
In order to make the degree of deformation or rubber elasticity of the rubber lip section particularly preferable, the spring hardness of the rubber material composition is set so as to fall within a range of 70 to 80.
In order to cause the contact seal device to quickly follow reciprocal movement of a movement section of the linear motion apparatus and to prevent occurrence of damage to the rubber lip section, the rubber material composition preferably has, along with the hardness specified above, a tensile breaking elongation of 200% or more and a tensile breaking strength of 13 Mpa or more as a mechanical strength.
A linear motion apparatus equipped with a contact seal device using the rubber material composition according to the present invention may have a lubricant supply member which is to be disposed in proximity to the contact seal device and is composed of lubricant-containing polymer.
The lubricant-containing polymer is formed from synthetic resin selected from a polyolefin-based resin group comprising polyethylene, polypropylene, polybutene, and polymethylpentene, which have essentially identical chemical constructions. A feedstock is formed by means of adding, to the synthetic resin and as a lubricant, paraffin-based hydrocarbon oil such as a poly-xcex1-olefin oil, a naphthene-based hydrocarbon oil, mineral oil, ether oil such as dialkyl phenyl ether oil, or ester oil such as ester-phthalate, solely or in combination. The feedstock is heated to a melting point of resin or higher until it becomes plasticized. The thus-plasticized feedstock is cooled into a solid form. Various additives, such as an oxidation inhibitor, a rust inhibitor, an abrasion inhibitor, a defoaming agent, and an extreme-pressure agent, may be added to the lubricant beforehand.
A composition ratio of lubricant-containing polymer comprises 10 to 50 wt. % polyolefin-based resin and 90 to 50 wt. % lubricant with respect to the total weight of the polymer. When polyolefin-based resin assumes a value of less than 10 wt. %, hardness or strength of a certain level or higher cannot be attained. Hence, there arises an increase in the possibility of a problem, such as damage, occurring when load is imposed on the contact seal device as a result of actuation of the linear motion apparatus. When polyolefin-based resin exceeds 50 wt. % or more (i.e., when a lubricant accounts for less than 50 wt. %), supply of a lubricant to the rubber lip section is lessened, thereby diminishing an effect of reducing abrasion of the rubber lip section
The group of synthetic resin has the same basic construction but changes in mean molecular weight within the range of 700 to 5xc3x97106. Synthetic resin having a mean molecular weight of 700 to 1xc3x97104 (e.g., polyethylene wax), synthetic resin having a comparatively-low molecular weight of 1xc3x97104 to 1xc3x97106, and synthetic resin classified into a wax having a ultrahigh molecular weight of 1xc3x97106 to 5xc3x97106 are used solely or in combination, as required. Through combination of synthetic resin of comparatively low molecular weight with a lubricant, there is produced lubricant-containing polymer having a certain level of mechanical strength, lubricant supply capability, and an oil retaining characteristic.
When some of the synthetic resin of comparatively low molecular weight are replaced with synthetic resin to be classified into a wax, an affinity for lubricating oil is increased, because of a small difference between the synthetic resin to be classified into a wax and the lubricating oil. Consequently, the oil retaining characteristic of the lubricant-containing polymer is improved, thereby enabling long-term supply of a lubricant. However, the mechanical strength of the polymer is deteriorated.
In addition to polyolefin-based resin such as polyethylene wax, hydrocarbon based wax having a fusing point from 100 to 130xc2x0 C. or more (e.g., paraffin-based synthetic wax) can be preferably used as wax. If some of the synthetic resin of comparatively low molecular weight is replaced with synthetic resin of ultrahigh molecular weight, an affinity for lubricating oil is decreased, because of a great difference (in molecular weight) between the synthetic resin of ultrahigh molecular weight and the lubricating oil. Consequently, the oil retaining characteristic of the lubricant-containing polymer and seepage of a lubricant from the lubricant-containing polymer become faster.
As a result, the time that elapses before the amount of lubricant which can be supplied from the lubricant-containing polymer to the bearing becomes shorter, thus shortening the life of a bearing. However, the mechanical strength of the polymer is increased.
In consideration of a balance between ease of moldability, mechanical strength, oil retaining characteristic, and the amount of lubricant to be supplied, the composition ratio of lubricant-containing polymer preferably comprises 0 to 5 wt. % synthetic resin to be classified into a wax; 8 to 48 wt. % synthetic resin of comparatively low molecular weight; 2 to 15 wt. % synthetic resin of ultrahigh molecular weight; and 10 to 50 total wt. % of three types of resins (i.e., a lubricant accounts for a remaining; that is, 90 to 50 wt. %).
In order to improve mechanical strength of a lubricant-containing polymer, thermoplastic resin and thermosetting resin such as those mentioned below may be added to the polyolefin-based resin.
As thermoplastic resin, there can be used polyamide, polycarbonate, polyethylene terephthalate, polyphenylene sulfide, polyether sulfone, polyether ether ketone, polyamideimide, polystyrene, and ABS resin.
As thermoplastic resin, there can be used unsaturated polyester resin, urea resin, melamine resin, phenol resin, polyimide resin, or epoxy resin.
These resins may be used solely or in combination.
In order to disperse polyolefin-based resin and other resin more uniformly, an appropriate compatibilizer may be added to the resins.
In order to improve the mechanical strength of the resin, a filler may be added to the resin. For instance, there may be added calcium carbonate, magnesium carbonate, inorganic whiskers such as potassium titanate whiskers or aluminum borate whiskers, inorganic fibers such as glass fibers or metal fibers, or a braided fabric consisting of an inorganic fiber. In the case of organic compounds, carbon black, graphite powder, carbon fiber, aramid fiber, or polyester fiber may be added.
In order to prevent deterioration of polyolefin-based resin, which would otherwise be caused by heat, there may be added antioxidant such as N,Nxe2x80x2-diphenyl-P-phenyldiamine, 2,2xe2x80x2-methylenebis(4-ethyl-6-t-butylphenol). In order to prevent deterioration of the polyolefin-based resin, which would otherwise be caused by light, there may be added an ultraviolet absorbent such as 2-hydroxy-4-n-octoxybenzophenone, 2-(2xe2x80x2-hydroxy-3xe2x80x2-t-butyl-5xe2x80x2-methyl-phenyl)-5-chlorobenzotriazole.
The total amount of all additives (excluding polyolefin-based resin and the lubricant) is preferably 20 wt. % or less the total amount of molding feedstock, in terms of preservation of capability of supplying a lubricant.
In addition, it is an object of the second aspect of the present invention to provide a bearing for a water pump equipped with a seal device which does not become deformed even when used in a high-temperature atmosphere or upon contact with excessive cooling water.
The object of the invention is achieved by a bearing for a water pump including an outer ring fastened to a casing, a rotating shaft having at one end a driven section and at the other end an impeller, rolling elements interposed between the outer ring and the rotating shaft, and a pair of seal device fastened to respective ends of the outer ring and respectively having elastic material, thereby sealing a space between the rotating shaft and the bearing, wherein elastic material of at least the seal device disposed so as to oppose the impeller is formed from a vulcanizable fluoro rubber composition containing vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer or from a vulcanizable fluoro rubber composition containing tetrafluoroethylene-polypropylene copolymer.
Since the vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer is a ternary system and contains a relatively-low proportion of vinylidene fluoride. Further, since the vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer does not contain hexafluoropropylene, a basic compound, such as amine, is less apt to induce removal of hydrofluoric acid from vinylidene fluoride. The tetrafluoroethylene-polypropylene copolymer does not contain vinylidene fluoride as raw material. As in the case of the vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer, the tetrafluoroethylene-polypropylene copolymer does not contain hexafluoropropylene. For this reason, a basic compound, such as amine, is less apt to induce removal of hydrofluoric acid from vinylidene fluoride. Accordingly, the tetrafluoroethylene-polypropylene copolymer is suitable as elastic material of the seal device of the water pump bearing. These fluoro rubbers are much superior in chemical resistance to standard fluoro rubber (e.g., vulcanizable fluoro rubber composition containing vinylidenefluoride-hexafluoropropylen copolymer or vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene terpolymer). More specifically, when vulcanizable fluoro rubber composition containing vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer or vulcanizable fluoro rubber composition containing tetrafluoroethylene-polypropylene copolymer is used as elastic material of the seal device of the water pump bearing, the seal device is not denatured and can make full use of superior sealing performance over a long period of time even when used in a high-temperature ambient or upon contact with cooling water. Hence, entry of seam into the bearing is prevented, thus avoiding a drop in the performance of the bearing.
Further, it is an object of the third aspect of the present invention to improve durability of a rubber seal device employed in a rolling bearing which is exposed to a synthetic cutting coolant of soluble type that is particularly suitable for high-speed machining or as an automobile coolant, and also to improve durability of a rubber seal device employed in a rolling bearing having urea-based grease sealed therein, as well as providing a long-life rolling bearing.
The above-mentioned object can be attained by a rolling bearing, according to the third aspect of the present invention, including at least an inner ring, an outer ring, rolling elements, a retainer, and a rubber seal device, wherein
the rubber seal device is formed integrally from a fluoro rubber composition containing at least one of vinylidenefluoride-tetrafluoroethylene-polypropylene terpolymer and tetrafluoroethylene-polypropylene copolymer, and a reinforcing member.